This application claims the priority benefit of Taiwan application serial no. 90120809, filed Aug. 24, 2001.
1. Field of the Invention
The invention relates in general to a light emitting diode (LED), and more particularly, to a driving method of an organic light emitting diode (OLED).
2. Description of the Related Art
To comply with the need for more versatile information equipment, the demand for flat panel displays (FPD) is rapidly increasing. The current trends of being light, thin, short and small have resulted in the replacement of cathode ray tubes (CRT) with flat panel displays. Currently, the major application of flat panel displays includes plasma display, liquid crystal display, electroluminescent display, light emitting diode, vacuum fluorescent display, field emission display, electrochromic display and organic light emitting diode.
The organic light emitting diode is further categorized into two types, a small molecular type and a polymer type. Due to the characteristics of (1) unlimited vision angle; (2) low fabrication cost; (3) high response speed (hundreds of times for the liquid crystal); (4) power saving; (5) drivable by direct current of portable machines; (6) wide temperature range; (7) light weight and sizable according to hardware specifications, the organic light emitting diode is meeting the requirements of the multimedia regime. Therefore, the organic light emitting diode possesses great potential in the flat panel display system and is the flat panel display for the next generation.
The driving method of the organic light emitting diode is not constant. Typically, the conducting voltage of the organic light emitting diode is 2.4V. In an array of organic light emitting diodes, a forward bias is applied to the light emitting diode which is to emit a light. For example, 6V is applied to the positive electrode and 0V is applied to the negative electrode. The organic light emitting diodes which do not emit are applied with a reverse bias. Normally, the pins of the remaining organic light emitting diodes are floating or connected to an unknown voltage, so that the organic light emitting diodes which do not emit are turned off. Alternatively, the current LCD driving chip can be used to drive the organic light emitting diodes. However, problems occur due to the difference between the structures.
Due to the unsure and incorrect driving method, the light emitting diode which is not supposed to illuminate emits a light. As a result, the organic light emitting diode panel cannot be driven normally. The different driving methods cause too much power consumption.
The invention provides a driving circuit and a driving method of an organic light emitting diode. A simple way to drive the organic light emitting diode panel is employed to enable the organic light emitting diode to illuminate. The units which are not supposed to illuminate are turned off without driving errors.
The driving circuit and method for an organic light emitting diode can also effectively reduce the power consumption.
In the driving circuit and method of an organic light emitting diode provided by the invention, an array with a plurality of light emitting diodes is provided. The array has a plurality of rows and columns. The column and row of a light emitting diode is selected. A first voltage is applied to the selected row, and a second voltage is applied to the selected column. A voltage difference between the first and second voltages is larger than a conducting voltage of the organic light emitting diodes. The selected light emitting diode can thus illuminate. Meanwhile, the first and second voltages are respectively applied to the remaining rows and columns which are not connected to the selected organic light emitting diode.
The invention provides another driving method of an organic light emitting diode applied to an array of a plurality of organic light emitting diodes. The array has a plurality of rows and a plurality of columns. The column and row of a light emitting diode is selected. A first voltage is applied to the selected row, and a second voltage is applied to the selected column. A voltage difference between the first and second voltages is larger than a conducting voltage of the organic light emitting diodes. The selected light emitting diode can thus illuminate. Meanwhile, a third and a fourth voltages are respectively applied to the remaining rows and columns which are not connected to the selected organic light emitting diode. Thereby, a reverse bias is applied to all the light emitting diodes which are not selected.
In the above method, the voltage difference between the first voltage and the second voltage is no less than the conducting voltage. The voltage difference between the first and third voltages is no larger than the conducting voltage. The voltage difference between the fourth and the third voltages is no larger than the conducting voltage.
The invention also provides a driving circuit of an organic light emitting diode including a plurality of organic light emitting diodes, a plurality of first voltage selectors and a plurality of second voltage selectors. The organic light emitting diodes are arranged as an array with a plurality of rows and a plurality of columns. The first voltage selectors are coupled to the columns of the array and select between the first and second voltages supplying to each column. The first voltage is larger than the second voltage. The second voltage selectors are connected to the rows of the array. The second voltage selectors are coupled to the rows of the array and select between the third and fourth voltages to supply to each row. The third voltage is larger than the fourth voltage. The voltage difference between the first voltage and the second voltage is not smaller than the conducting voltage of each of the organic light emitting diodes. The voltage difference between the fourth voltage and the second voltage is not larger than the conducting voltage. The voltage difference between the fourth and the third voltages is no larger than the conducting voltage.
Thereby, only the voltage across the organic light emitting diode to illuminate is larger than the conducting voltage. The voltages across the remaining organic light emitting diodes are smaller than the conducting voltage to ensure only the selected organic light emitting diode illuminates, while the neighboring light emitting diodes do not illuminate due to interference.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.